1. Field of the Invention
The subject invention relates to plasma processing chambers and, more specifically, to plasma processing chambers having at least twin or tandem processing regions enabling processing of at least two substrates simultaneously.
2. Related Art
In the fabrication of semiconductor wafers, two types of semiconductor processing systems are commonly employed. The first type of systems commonly used is generally referred to as batch processing systems. The chief reason behind development of batch processing systems is that several wafers are processed simultaneously, thereby providing high throughput. However, with the tightening of performance specifications, the industry has moved to the second type of processing chambers, i.e., single-wafer processing chambers. The chief reason for development of single wafer processing systems is that it is easier to control the process characteristics and uniformity across the wafer.
On the other hand, in some niche applications, attempts have been made to produce a processing chamber capable of processing two wafers at a time. The idea behind this approach is to enable single-wafer processing characteristics, while producing two wafers at a time. One configuration for twin/tandem wafer processing is disclosed in U.S. Pat. No. 5,811,022, which discloses an inductively coupled plasma chamber used for plasma photoresist removal, also known as photoresist ashing. Photoresist ashing is a process of oxidation reaction in which oxygen is used to remove organic photoresists. The photoresist is oxidized into gases such as carbon monoxide, carbon dioxide, and water vapor, and then removed by vacuum pump. Consequently, such application need not have high accuracy of process uniformity over the wafer as more critical applications, such as semiconductor wafer etching.
Since the process requirements of photoresist ashing are not stringent, the chamber proposed in the '022 patent includes two separate plasma generation chambers, both of which being open at the bottom to a wafer processing chamber that houses two wafers. A charged particle filter is provided between the plasma chambers and the processing chamber, so as to prevent charged particles from reaching the processing chamber, but allowing neutral activated species to reach the processing chamber to remove the photoresist from the wafers. Since the processing chamber is constructed so that there is no separation between the two wafers and no plasma can be ignited over the wafers, and further since a filter is provided to remove charged particles from the wafer processing chamber, the chamber of the '022 patent cannot be used for modern critical application, such as semiconductor wafer etching, but only for simple ashing.
Another tandem processing chamber is disclosed in, e.g., U.S. Pat. No. 5,855,681. The processing chamber disclosed in the '681 patent includes two processing regions for simultaneously processing two wafers, and “include[s] separate gas distribution assemblies and RF power sources to provide uniform plasma density over a wafer surface in each processing region.” Notably, the authors of the '681 patent explain that the unsatisfactory result provided by the Mattson system (the subject of the '022 patent described above) “is a direct result of having multiple wafers being partially processed at multiple stations within a single chamber.” To improve upon this design, the authors of the '681 teach that the chamber should have “isolated processing regions” so as to have “isolated processes [ ] performed concurrently in at least two regions so that at least two wafers can be processed simultaneously.”
While the solution of isolating the processing regions enables tandem processing of two wafers simultaneously, it introduces difficulties in what is commonly referred to as chamber matching or station matching. That is, it becomes difficult to control the two processing regions of the chamber to provide identical plasma processing conditions. For example, if one processing region develops higher etch rate than the other region, it becomes difficult to control the endpoint of the etch process. That is, if the end point is determined according to the higher etch rate side, then the wafer of the other side would not be fully etched. On the other hand, if the end point is delayed, then the wafer at the higher etch rate region may be over etched and be damaged.
A modified version of this tandem chamber is disclosed in, e.g., U.S. Pat. No. 6,962,644, which teaches “a chamber defining a plurality of isolated processing regions.” In the '644 patent a “central pumping plenum” enables the two chambers “to communicate with each other,” which leads to a problem known in the art as RF “crosstalk.” RF cross talk is deleterious for tandem processing as conditions change in one processing region adversely effect the processing in the second tandem region.
The isolated tandem chambers described above still have the problem in that due to the isolation, it is hard to match the process results between the two processing regions. Additionally, the tandem chamber described in the '644 patent uses two RF power suppliers that are phase and frequency locked to prevent beating of the RF power from the two sources. This complicates the structure and construction of the chamber. Finally, the method for generating plasma in the tandem chambers described above fail to provide the tight performance specifications required for fabricating advanced semiconductor devices. Accordingly, there is a need in the art for a multiple-wafers chamber that enables high level of performance, while matching the performance in each processing region of the chamber.